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Composites Terminology Database

This glossary is not an exhaustive list, however it does contain the majority of terms used in the composites industry and as part of the management of our website, it is updated on a continual basis.

The terms are accessed by clicking on the appropriate letter below, all the terms beginning with the letter F can be found below.

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Terms F

Click on a term and it will take you to the coresponding explanation.

fabric fill face
That side of the woven fabric where the greatest number of the yarns are perpendicular to the selvage.

fabric prepreg batch
Prepreg containing fabric from one fabric batch, impregnated with one batch of resin in one continuous operation.

fabric warp face
That side of the woven fabric where the greatest number of the yarns are parallel to the selvage.

fabric, non-woven
See: non-woven fabric

fabric, woven
See: woven fabric

A member or structure, the primary function of which is to streamline the flow of a fluid by producing a smooth outline and to reduce drag, as in aircraft frames and boat hulls.

fatigue life
The number of cycles of deformation required to bring about failures of the test specimen under a given set of oscillating conditions (stresses or strains).

fatigue limit
The stress level below which a material can be stressed cyclically for an infinite number of times without failure.

fatigue ratio
The ratio of fatigue strength to tensile strength. Mean stress and alternating stress must be stated.

fatigue strength
The maximum cyclical stress a material can withstand for a given number of cycles before failure occurs. The residual strength after being subjected to fatigue.

The failure or decay of mechanical properties after repeated applications of stress. Fatigue tests give information on the ability of a material to resist the development of cracks, which eventually bring about failure as a result of a large number of cycles.

faying surface
The surfaces of materials in contact with each other and joined or about to be joined together.

A fibrous material made up of interlocked fibres by mechanical or chemical action, moisture, or heat. Made from fibres such as asbestos, cotton, glass, and so forth. See also fibre. A general term used to refer to filamentary materials, often, fibre is used synonymously with filament. It is a general term for a filament with a finite length that is at least 10 times its diameter, which is typically 1 to 13 mm (0.004 to 0.005 in.).

In most cases it is prepared by drawing from a molten bath, spinning, or deposition on a substrate. A whisker, on the other hand, is a short single-crystal fibre or filament made from a wide variety of materials, with diameters ranging from 1 to 25µm (40 to 1400 µin.) and aspect ratios (a measure of length) between 100 and 15 000. Fibres can be continuous or specific short lengths (discontinuous), normally no less than 3.2 mm ( 1/8 in.).

fibre content
The amount of fibre present in a composite. This is usually expressed as a percentage volume fraction or weight fraction of the composite.

fibre count
The number of fibres per unit width of ply present in a specified section of a composite.

fibre diameter
The measurement (expressed in hundred thousandths) of the diameter of individual filaments.

fibre direction
The orientation or alignment of the longitudinal axis of the fibre with respect to a stated reference axis.

fibre pattern
Visible fibres on the surface of laminates or moulding. The thread size and weave of glass cloth.

fibre show
Strands or bundles of fibres that are not covered by plastic, and that are at or above the surface of a composite.

fibre wash
Splaying out of woven or non-woven fibres from the general reinforcement direction. Fibres are carried along with bleeding resin during cure.

fibre-reinforced plastic (FRP)
A general term for a composite that is reinforced with cloth, mat, strands, or any other fibre form.

fibreglass reinforcement
Major material used to reinforce plastic. Available as mat, roving, fabric, and so forth. It is incorporated into both thermosets and thermoplastics.

An individual filament made by drawing molten glass. A continuous filament is a glass fibre of great or indefinite length. A staple fibre is a glass fibre of relatively short length, generally less than 430 mm ( 17 in.), the length related to the forming or spinning process used.

The smallest unit of a fibrous material. The basic units formed during drawing and spinning, which are gathered into strands of fibre for use in composites. Filaments usually are of extreme length and very small diameter, usually less than 75 µm (1 mil). Normally filaments are not used individually. Some textile filaments can function as a yarn when they are of sufficient strength and flexibility.

Yarn oriented at right angles to the warp in a woven fabric.

A relatively inert substance added to a material to alter its physical, mechanical, thermal, electrical, and other properties or to lower cost or density. Sometimes the term is used specifically to mean particulate additives.
See: inert filler

A rounded filling or adhesive that fills the corner or angle where two adherents are joined.

filling yarn
The transverse threads or fibres in a woven fabric. Those fibres running perpendicular to the warp. Also called weft

film adhesive
A synthetic resin adhesive, usually of the thermosetting type, in the form of a thin dry film of resin with or without a paper or glass carrier.

A mixture of materials for treating glass or other fibres. It contains a coupling agent to improve the bond of resin to the fibre, and usually includes a lubricant to prevent abrasion, as well as a binder to promote strand integrity. With graphite or other filaments, it may perform any or all of the above functions.

first-order transition
A change of state associated with crystallisation or melting in a polymer.

flame resistance
Ability of a material to extinguish flame once the source of heal is removed. See: self-extinguishing resin

flame retardants
Certain chemicals that are used to reduce or eliminate the tendency of a resin to burn.

Measure of the extent to which a material will support combustion.

That portion of the charge which flows from or is extruded from the mould cavity during the moulding. Extra plastic attached to a moulding along the parting line, which must be removed before the part is considered finished.

flat panel
Flat, thin panel, frequently of the sandwich type.

An additive that makes a finished plastic more flexible or tough. See: plasticiser

flexible moulds
Moulds made of rubber or elastomeric plastics, used for casting plastics. They can be stretched to remove cured pieces with undercuts.

flexural strength
The maximum stress that can be borne by the surface fibres in a beam in bending. The flexural strength is the unit resistance to the maximum load before failure by bending, usually expressed in force per unit area.

flow line
A mark on a moulded piece made by the meeting of two flow fronts during moulding. Also called striae, weld mark, or weld line

flow marks
Wavy surface appearance of an object moulded from thermoplastic resins, caused by improper flow of the resin into the mould.

The movement of resin under pressure allowing it to fill all parts of a mould. The gradual but continuous distortion of a material under continued load, usually at high temperatures; also called creep

fluted core
An integrally woven reinforcement material consisting of ribs between two skins in a unitised sandwich construction.

Refers to the deposition of foams when the foaming machine must be brought to the work that is "in place," as opposed to bringing the work to the foaming machine. Also, foam mixed in a container and poured into a mould, where it rises to fill the cavity.

foamed plastics
Resins in sponge form, flexible or rigid, with cells closed or interconnected and density over a range from that of the solid parent resin to 0.030 g/cm. Compressive strength of rigid foams is fair, making them useful as core materials for sandwich constructions. Also, a chemical cellular plastic, the structure of which is produced by gases generated from the chemical interaction of its sandwich constituents

foaming agent
Chemicals added to plastics and rubbers that generate inert gases on heating, causing the resin to assume a cellular structure.

The male half of the mould that enters the cavity, exerting pressure on the resin and causing it to flow. Also called punch.

FP fibre
Polycrystalline alumina fibre (Al2O3). A ceramic fibre useful for high temperature (1370 to 1650°ree; C. or 2500 to 3000°ree; F) composites.

fracture stress
The true, normal stress on the minimum cross-sectional area at the beginning of fracture.

fracture toughness
A measure of the damage tolerance of a material containing initial flaws or cracks. Used in aircraft structural design and analysis.

The separation of a body. Defined both as rupture of the surface without complete separation of laminate and as complete separation of a body because of external or internal forces.

free wall
The portion of a honeycomb cell wall that is not connected to another cell.

free-radical polymerisation
A type of polymerisation in which the propagating species is a long-chain free radical initiated by the introduction of free radicals from thermal or photochemical decomposition.

friction, coefficient of

"coefficient of friction"


"fibre-reinforced plastic"

fungus resistance
The resistance of a material to attack by fungi in conditions promoting their growth.

Accumulation of short broken filaments after passing glass strands, yarns, or rovings over a contact point. Often weighted and used as an inverse measure of abrasion resistance.

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